1. Field of the Invention
The present invention relates to the vehicle positioning technology and more particularly, to an accurate positioning system for a vehicle and its positioning method.
2. Description of Related Art
FIG. 1 is a schematic drawing showing a car equipped with a GPS navigation system. As illustrated, the GPS navigation system comprises a GPS (Global Position System) 81 and a navigation device 82. The GPS 81 is adapted to receive and analyze signals from multiple GPS satellites to determine the co-ordinates data of the car. The microprocessor 821 of the navigation device 82 compares the co-ordinates data obtained from the GPS 81 with its built-in electronic map database (e-Map database) 822, thereby determining the location of the car on the earth and showing a sign representing the car on the map that is displayed on the display 83 corresponding to the location of the car on the earth to help the driver navigate the car.
The GPS 81 receives and analyzes signals from multiple GPS satellites to determine the co-ordinates data of the car, and outputs the co-ordinates data of the car once per second. However, when the car is running at a high speed, the long time interval of outputting the co-ordinates data of the car once per second may result in a big error. If the microprocessor 821 compares the inaccurate co-ordinates data of the car to the built-in electronic map database 822, the microprocessor 821 will allocate the sign representing the car on the map at an inaccurate location and thus give a wrong navigation. Further, when the car passes along a tunnel, the GPS 81 cannot receive signals from the GPS satellites and will output inaccurate co-ordinates data, thereby causing the car to be unable to obtain the accurate position. Therefore, there is still room for improvement in the GPS devices for determining vehicle location.